WaterCAD is described as 'Water Distribution Modeling and Management'. There are four alternatives to WaterCAD for Windows, Linux, Mac and Wine. The best alternative is EPANET, which is both free and Open Source. Other great apps like WaterCAD are pfcalc (Free, Open Source), fluids (Free, Open Source) and InfoWater (Paid).
pfcalc stands for pipe friction calculator and is a CLI program that computes pressure drop in piping systems using the Darcy-Weisbach equation. The program is capable of computing minor and major pressure losses for flow in pipes and ducts.